1. Field of the Invention
This invention relates generally to the field of remote power control systems, and more particularly to using a data communications link for power control.
2. Description of the Related Art
Many computer systems and peripheral equipment are located out of reach of service personnel, such as at unmanned locations. Even when they are within reach it is often desirable to have computer systems maintain power control over themselves and their peripherals; this makes operations even more energy efficient and avoids operator error in power down situations.
Once all power is physically removed from any unit, the unit is unable to perform any functions and therefore cannot return to a powered state unless the flow of power is restored by another unit.
Lap-top computers often selectively reduce their own power consumption based upon user needs. For instance, a lap-top computer may place the screen in a low power or no power state if the computer is not in use. Hard disk drives are often treated similarly. When the microprocessor, by some predetermined event, determines that power needs to be restored, the flow of power is returned to the unit. Components are often driven into various power states by such a power controller. Many video cassette recorders (VCRs), when turned off, are actually in a low power state, ready to power up and begin recording at the instance of some event, usually a prespecified time or the touch of the power button on the units remote control. The controlling device remains in the power on state and monitors for any such event. Large electronic systems with greater power consumption needs can also take advantage of the energy efficiency and the reduction in operator error of a power control system.
In a computer system, in order for one unit to have power control over another, there must also be a relationship between them such that the controller (master) will not remove power from a controlled (slave) until the slave is in a state ready to be powered down. If a single slave unit is controlled by multiple masters, there will have to be some mechanism for preventing the slave from having power removed while serving another master.
To accomplish this, a hardware protocol can be implemented through the use of a dedicated power control interface; when any master needs the services of a slave it simply supplies power to a particular line in the interface. When the master is no longer in need of the slave it simply stops asserting that power. All masters use a common interface line for this action, therefore, when that line is without power the slave is powered off because no master requires its services.
Data communications equipment may be used to control power to host equipment. To do this a transceiver with a built in frame decoder may be left powered on, the host remains in a power off state until a properly addressed power-up frame is received. Once such a frame is received the host is supplied with power until a properly addressed power-down frame is detected.
A different method for preventing a slave from having power removed while serving another master is through the use of a protocol that builds power allegiances between the slave and each master being serviced. A power allegiance is built by a master sending a power-on frame to an intelligent frame decoder. In response, the frame decoder supplies power to the requested device. If another power-on frame is received from different source another power allegiance is built without the need to change the supply of power to the device. When a power-off frame is received, the corresponding power allegiance is broken. If, upon receipt of a power-off frame and the breaking of that power allegiance, there are no other power allegiances for that device, the supply of power to that device is terminated.